The pneumatic boats of relatively large dimensions, having, for instance, a length of four to eight meters and designed for conveying an appropriate number of people or a suitable quantity of cargo as well as for advancing to a considerable distance from the coast, are mainly provided, notoriously, with a floating body including a certain number of air chambers inflatable by means of compressed air, which are suitably arranged within a protective covering envelope.
So long as the boat length does not exceed three or four meters, the task of playing the double function of "keel" and of "deck" can be entrusted advantageously to one straightening element only, which has to be rigid or opportunely stiffened. If the boat length surpasses these values, the employment of only one straightening element results in some considerable difficulties indeed.